There have been many proposals and developments for analyzing materials by absorption edge analysis such as K-edge analysis. Pertinent examples are found in the U.S. Pat. Nos. 3,100,261 Bigelow, 3,114,832 Alvarez and 3,701,899 Voparil.
U.S. Pat. Nos. 3,904,876 Arendt and 4,081,676 Buchnea set out two proposals for commercial multicomponent paper ash analyzers, while U.S. Pat. No. 4,090,074 Watt contains a proposal for determining coal ash content and ash components.
Two articles by Cho, B. Y. and Utt, O. L., "A New TiO.sub.2 Compensated X-Ray Ash Sensor for Paper," a preprint No. 75-611 of a paper presented at the Instrument Society of America, Industry Oriented Conference and Exhibit, Milwaukee, Wis., Oct. 6-9, 1975, and "Composition Compensated Paper Ash Gauge," a preprint of a paper presented at the ERDA Symposium on X- and Gamma-Ray Sources and Applications, Ann Arbor, Mich., May 19-21, 1976, describe a single-channel x-ray gauge, for paper, that measures the total ash content in binary ash-forming mixtures such as titanium dioxide and calcium carbonate, calcium carbonate and clay, or clay and commercial success, it is frequently desired to be able to separately measure the individual components of the ash forming constituent in the paper. For example, if the ash constituent consists of clay and titanium dioxide, since the titanium dioxide is a much more expensive ingredient than the clay, it may be desired to continuously determine, from measurements of the traveling paper sheet per se, what fraction or percentage of the paper or ash forming material weight is titanium dioxide and/or what percentage or fraction is clay. It is also desired to be able to measure the total ash content of paper wherein the ash forming constituent is a tertiary mixture of clay, calcium carbonate and titanium dioxide, for example, or perhaps the content of one or more of these individual components in the paper may be of interest.
In laboratories, discrete static samples of material are commonly analyzed by taking several measurements with different wavelengths of well-monochromatized radiation. Fluorescent radiators and/or diffractometers, as well as certain radioisotope sources may be used to obtain the effectively monoichromatic rays that may be initially directed into the sample, and diffractometers and/or energy selective detection apparatus, possibly using a multichannel analyzer, may be used to evaluate the intensity of different wavelengths received from the sample. Digital computers facilitate the mathematical process of converting the signal intensity information to quantitative valves indicative of the content of various components in the sample.
Since relatively fast and powerful digital computers have come into common use as an aid to the measurement and control of continuous industrial processes such as paper manufacture, there have been proposals to adapt these and similar laboratory techniques to the analysis of multicomponent materials during production. In a complex problem such as paper ash component analysis, the mathematical equations are frequently unsolvable, but solutions may be theoretically possible using iterative computations. Hence in some theoretical discussions of these proposals it is sometimes implied that ash component analysis, for example, can be usefully performed on line during the paper making process. As a matter of fact, however, with the practical radiation intensity limitations on usable sources and detectors, there simply is not sufficient integration time available on line to obtain reliable ash component analyses using these adaptations of the laboratory methods. They are thus generally limited in practical application to the measurement of total ash in a binary ash constituent mixture, a task which the apparatus of Utt and Cho, supra, has been able to perform in a much simpler and more reliable manner.